LCOV - code coverage report
Current view: top level - include/linux - dcache.h (source / functions) Hit Total Coverage
Test: coverage.info Lines: 10 30 33.3 %
Date: 2023-04-06 08:38:28 Functions: 0 0 -

          Line data    Source code
       1             : /* SPDX-License-Identifier: GPL-2.0 */
       2             : #ifndef __LINUX_DCACHE_H
       3             : #define __LINUX_DCACHE_H
       4             : 
       5             : #include <linux/atomic.h>
       6             : #include <linux/list.h>
       7             : #include <linux/math.h>
       8             : #include <linux/rculist.h>
       9             : #include <linux/rculist_bl.h>
      10             : #include <linux/spinlock.h>
      11             : #include <linux/seqlock.h>
      12             : #include <linux/cache.h>
      13             : #include <linux/rcupdate.h>
      14             : #include <linux/lockref.h>
      15             : #include <linux/stringhash.h>
      16             : #include <linux/wait.h>
      17             : 
      18             : struct path;
      19             : struct file;
      20             : struct vfsmount;
      21             : 
      22             : /*
      23             :  * linux/include/linux/dcache.h
      24             :  *
      25             :  * Dirent cache data structures
      26             :  *
      27             :  * (C) Copyright 1997 Thomas Schoebel-Theuer,
      28             :  * with heavy changes by Linus Torvalds
      29             :  */
      30             : 
      31             : #define IS_ROOT(x) ((x) == (x)->d_parent)
      32             : 
      33             : /* The hash is always the low bits of hash_len */
      34             : #ifdef __LITTLE_ENDIAN
      35             :  #define HASH_LEN_DECLARE u32 hash; u32 len
      36             :  #define bytemask_from_count(cnt)       (~(~0ul << (cnt)*8))
      37             : #else
      38             :  #define HASH_LEN_DECLARE u32 len; u32 hash
      39             :  #define bytemask_from_count(cnt)       (~(~0ul >> (cnt)*8))
      40             : #endif
      41             : 
      42             : /*
      43             :  * "quick string" -- eases parameter passing, but more importantly
      44             :  * saves "metadata" about the string (ie length and the hash).
      45             :  *
      46             :  * hash comes first so it snuggles against d_parent in the
      47             :  * dentry.
      48             :  */
      49             : struct qstr {
      50             :         union {
      51             :                 struct {
      52             :                         HASH_LEN_DECLARE;
      53             :                 };
      54             :                 u64 hash_len;
      55             :         };
      56             :         const unsigned char *name;
      57             : };
      58             : 
      59             : #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
      60             : 
      61             : extern const struct qstr empty_name;
      62             : extern const struct qstr slash_name;
      63             : extern const struct qstr dotdot_name;
      64             : 
      65             : /*
      66             :  * Try to keep struct dentry aligned on 64 byte cachelines (this will
      67             :  * give reasonable cacheline footprint with larger lines without the
      68             :  * large memory footprint increase).
      69             :  */
      70             : #ifdef CONFIG_64BIT
      71             : # define DNAME_INLINE_LEN 32 /* 192 bytes */
      72             : #else
      73             : # ifdef CONFIG_SMP
      74             : #  define DNAME_INLINE_LEN 36 /* 128 bytes */
      75             : # else
      76             : #  define DNAME_INLINE_LEN 40 /* 128 bytes */
      77             : # endif
      78             : #endif
      79             : 
      80             : #define d_lock  d_lockref.lock
      81             : 
      82             : struct dentry {
      83             :         /* RCU lookup touched fields */
      84             :         unsigned int d_flags;           /* protected by d_lock */
      85             :         seqcount_spinlock_t d_seq;      /* per dentry seqlock */
      86             :         struct hlist_bl_node d_hash;    /* lookup hash list */
      87             :         struct dentry *d_parent;        /* parent directory */
      88             :         struct qstr d_name;
      89             :         struct inode *d_inode;          /* Where the name belongs to - NULL is
      90             :                                          * negative */
      91             :         unsigned char d_iname[DNAME_INLINE_LEN];        /* small names */
      92             : 
      93             :         /* Ref lookup also touches following */
      94             :         struct lockref d_lockref;       /* per-dentry lock and refcount */
      95             :         const struct dentry_operations *d_op;
      96             :         struct super_block *d_sb;       /* The root of the dentry tree */
      97             :         unsigned long d_time;           /* used by d_revalidate */
      98             :         void *d_fsdata;                 /* fs-specific data */
      99             : 
     100             :         union {
     101             :                 struct list_head d_lru;         /* LRU list */
     102             :                 wait_queue_head_t *d_wait;      /* in-lookup ones only */
     103             :         };
     104             :         struct list_head d_child;       /* child of parent list */
     105             :         struct list_head d_subdirs;     /* our children */
     106             :         /*
     107             :          * d_alias and d_rcu can share memory
     108             :          */
     109             :         union {
     110             :                 struct hlist_node d_alias;      /* inode alias list */
     111             :                 struct hlist_bl_node d_in_lookup_hash;  /* only for in-lookup ones */
     112             :                 struct rcu_head d_rcu;
     113             :         } d_u;
     114             : } __randomize_layout;
     115             : 
     116             : /*
     117             :  * dentry->d_lock spinlock nesting subclasses:
     118             :  *
     119             :  * 0: normal
     120             :  * 1: nested
     121             :  */
     122             : enum dentry_d_lock_class
     123             : {
     124             :         DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
     125             :         DENTRY_D_LOCK_NESTED
     126             : };
     127             : 
     128             : struct dentry_operations {
     129             :         int (*d_revalidate)(struct dentry *, unsigned int);
     130             :         int (*d_weak_revalidate)(struct dentry *, unsigned int);
     131             :         int (*d_hash)(const struct dentry *, struct qstr *);
     132             :         int (*d_compare)(const struct dentry *,
     133             :                         unsigned int, const char *, const struct qstr *);
     134             :         int (*d_delete)(const struct dentry *);
     135             :         int (*d_init)(struct dentry *);
     136             :         void (*d_release)(struct dentry *);
     137             :         void (*d_prune)(struct dentry *);
     138             :         void (*d_iput)(struct dentry *, struct inode *);
     139             :         char *(*d_dname)(struct dentry *, char *, int);
     140             :         struct vfsmount *(*d_automount)(struct path *);
     141             :         int (*d_manage)(const struct path *, bool);
     142             :         struct dentry *(*d_real)(struct dentry *, const struct inode *);
     143             : } ____cacheline_aligned;
     144             : 
     145             : /*
     146             :  * Locking rules for dentry_operations callbacks are to be found in
     147             :  * Documentation/filesystems/locking.rst. Keep it updated!
     148             :  *
     149             :  * FUrther descriptions are found in Documentation/filesystems/vfs.rst.
     150             :  * Keep it updated too!
     151             :  */
     152             : 
     153             : /* d_flags entries */
     154             : #define DCACHE_OP_HASH                  0x00000001
     155             : #define DCACHE_OP_COMPARE               0x00000002
     156             : #define DCACHE_OP_REVALIDATE            0x00000004
     157             : #define DCACHE_OP_DELETE                0x00000008
     158             : #define DCACHE_OP_PRUNE                 0x00000010
     159             : 
     160             : #define DCACHE_DISCONNECTED             0x00000020
     161             :      /* This dentry is possibly not currently connected to the dcache tree, in
     162             :       * which case its parent will either be itself, or will have this flag as
     163             :       * well.  nfsd will not use a dentry with this bit set, but will first
     164             :       * endeavour to clear the bit either by discovering that it is connected,
     165             :       * or by performing lookup operations.   Any filesystem which supports
     166             :       * nfsd_operations MUST have a lookup function which, if it finds a
     167             :       * directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
     168             :       * dentry into place and return that dentry rather than the passed one,
     169             :       * typically using d_splice_alias. */
     170             : 
     171             : #define DCACHE_REFERENCED               0x00000040 /* Recently used, don't discard. */
     172             : 
     173             : #define DCACHE_DONTCACHE                0x00000080 /* Purge from memory on final dput() */
     174             : 
     175             : #define DCACHE_CANT_MOUNT               0x00000100
     176             : #define DCACHE_GENOCIDE                 0x00000200
     177             : #define DCACHE_SHRINK_LIST              0x00000400
     178             : 
     179             : #define DCACHE_OP_WEAK_REVALIDATE       0x00000800
     180             : 
     181             : #define DCACHE_NFSFS_RENAMED            0x00001000
     182             :      /* this dentry has been "silly renamed" and has to be deleted on the last
     183             :       * dput() */
     184             : #define DCACHE_COOKIE                   0x00002000 /* For use by dcookie subsystem */
     185             : #define DCACHE_FSNOTIFY_PARENT_WATCHED  0x00004000
     186             :      /* Parent inode is watched by some fsnotify listener */
     187             : 
     188             : #define DCACHE_DENTRY_KILLED            0x00008000
     189             : 
     190             : #define DCACHE_MOUNTED                  0x00010000 /* is a mountpoint */
     191             : #define DCACHE_NEED_AUTOMOUNT           0x00020000 /* handle automount on this dir */
     192             : #define DCACHE_MANAGE_TRANSIT           0x00040000 /* manage transit from this dirent */
     193             : #define DCACHE_MANAGED_DENTRY \
     194             :         (DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
     195             : 
     196             : #define DCACHE_LRU_LIST                 0x00080000
     197             : 
     198             : #define DCACHE_ENTRY_TYPE               0x00700000
     199             : #define DCACHE_MISS_TYPE                0x00000000 /* Negative dentry (maybe fallthru to nowhere) */
     200             : #define DCACHE_WHITEOUT_TYPE            0x00100000 /* Whiteout dentry (stop pathwalk) */
     201             : #define DCACHE_DIRECTORY_TYPE           0x00200000 /* Normal directory */
     202             : #define DCACHE_AUTODIR_TYPE             0x00300000 /* Lookupless directory (presumed automount) */
     203             : #define DCACHE_REGULAR_TYPE             0x00400000 /* Regular file type (or fallthru to such) */
     204             : #define DCACHE_SPECIAL_TYPE             0x00500000 /* Other file type (or fallthru to such) */
     205             : #define DCACHE_SYMLINK_TYPE             0x00600000 /* Symlink (or fallthru to such) */
     206             : 
     207             : #define DCACHE_MAY_FREE                 0x00800000
     208             : #define DCACHE_FALLTHRU                 0x01000000 /* Fall through to lower layer */
     209             : #define DCACHE_NOKEY_NAME               0x02000000 /* Encrypted name encoded without key */
     210             : #define DCACHE_OP_REAL                  0x04000000
     211             : 
     212             : #define DCACHE_PAR_LOOKUP               0x10000000 /* being looked up (with parent locked shared) */
     213             : #define DCACHE_DENTRY_CURSOR            0x20000000
     214             : #define DCACHE_NORCU                    0x40000000 /* No RCU delay for freeing */
     215             : 
     216             : extern seqlock_t rename_lock;
     217             : 
     218             : /*
     219             :  * These are the low-level FS interfaces to the dcache..
     220             :  */
     221             : extern void d_instantiate(struct dentry *, struct inode *);
     222             : extern void d_instantiate_new(struct dentry *, struct inode *);
     223             : extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
     224             : extern struct dentry * d_instantiate_anon(struct dentry *, struct inode *);
     225             : extern void __d_drop(struct dentry *dentry);
     226             : extern void d_drop(struct dentry *dentry);
     227             : extern void d_delete(struct dentry *);
     228             : extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);
     229             : 
     230             : /* allocate/de-allocate */
     231             : extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
     232             : extern struct dentry * d_alloc_anon(struct super_block *);
     233             : extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
     234             :                                         wait_queue_head_t *);
     235             : extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
     236             : extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
     237             : extern bool d_same_name(const struct dentry *dentry, const struct dentry *parent,
     238             :                         const struct qstr *name);
     239             : extern struct dentry * d_exact_alias(struct dentry *, struct inode *);
     240             : extern struct dentry *d_find_any_alias(struct inode *inode);
     241             : extern struct dentry * d_obtain_alias(struct inode *);
     242             : extern struct dentry * d_obtain_root(struct inode *);
     243             : extern void shrink_dcache_sb(struct super_block *);
     244             : extern void shrink_dcache_parent(struct dentry *);
     245             : extern void shrink_dcache_for_umount(struct super_block *);
     246             : extern void d_invalidate(struct dentry *);
     247             : 
     248             : /* only used at mount-time */
     249             : extern struct dentry * d_make_root(struct inode *);
     250             : 
     251             : /* <clickety>-<click> the ramfs-type tree */
     252             : extern void d_genocide(struct dentry *);
     253             : 
     254             : extern void d_tmpfile(struct file *, struct inode *);
     255             : 
     256             : extern struct dentry *d_find_alias(struct inode *);
     257             : extern void d_prune_aliases(struct inode *);
     258             : 
     259             : extern struct dentry *d_find_alias_rcu(struct inode *);
     260             : 
     261             : /* test whether we have any submounts in a subdir tree */
     262             : extern int path_has_submounts(const struct path *);
     263             : 
     264             : /*
     265             :  * This adds the entry to the hash queues.
     266             :  */
     267             : extern void d_rehash(struct dentry *);
     268             :  
     269             : extern void d_add(struct dentry *, struct inode *);
     270             : 
     271             : /* used for rename() and baskets */
     272             : extern void d_move(struct dentry *, struct dentry *);
     273             : extern void d_exchange(struct dentry *, struct dentry *);
     274             : extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
     275             : 
     276             : /* appendix may either be NULL or be used for transname suffixes */
     277             : extern struct dentry *d_lookup(const struct dentry *, const struct qstr *);
     278             : extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
     279             : extern struct dentry *__d_lookup(const struct dentry *, const struct qstr *);
     280             : extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
     281             :                                 const struct qstr *name, unsigned *seq);
     282             : 
     283             : static inline unsigned d_count(const struct dentry *dentry)
     284             : {
     285             :         return dentry->d_lockref.count;
     286             : }
     287             : 
     288             : /*
     289             :  * helper function for dentry_operations.d_dname() members
     290             :  */
     291             : extern __printf(3, 4)
     292             : char *dynamic_dname(char *, int, const char *, ...);
     293             : 
     294             : extern char *__d_path(const struct path *, const struct path *, char *, int);
     295             : extern char *d_absolute_path(const struct path *, char *, int);
     296             : extern char *d_path(const struct path *, char *, int);
     297             : extern char *dentry_path_raw(const struct dentry *, char *, int);
     298             : extern char *dentry_path(const struct dentry *, char *, int);
     299             : 
     300             : /* Allocation counts.. */
     301             : 
     302             : /**
     303             :  *      dget, dget_dlock -      get a reference to a dentry
     304             :  *      @dentry: dentry to get a reference to
     305             :  *
     306             :  *      Given a dentry or %NULL pointer increment the reference count
     307             :  *      if appropriate and return the dentry. A dentry will not be 
     308             :  *      destroyed when it has references.
     309             :  */
     310             : static inline struct dentry *dget_dlock(struct dentry *dentry)
     311             : {
     312           0 :         if (dentry)
     313           0 :                 dentry->d_lockref.count++;
     314             :         return dentry;
     315             : }
     316             : 
     317             : static inline struct dentry *dget(struct dentry *dentry)
     318             : {
     319          59 :         if (dentry)
     320          59 :                 lockref_get(&dentry->d_lockref);
     321             :         return dentry;
     322             : }
     323             : 
     324             : extern struct dentry *dget_parent(struct dentry *dentry);
     325             : 
     326             : /**
     327             :  *      d_unhashed -    is dentry hashed
     328             :  *      @dentry: entry to check
     329             :  *
     330             :  *      Returns true if the dentry passed is not currently hashed.
     331             :  */
     332             :  
     333             : static inline int d_unhashed(const struct dentry *dentry)
     334             : {
     335          52 :         return hlist_bl_unhashed(&dentry->d_hash);
     336             : }
     337             : 
     338             : static inline int d_unlinked(const struct dentry *dentry)
     339             : {
     340           0 :         return d_unhashed(dentry) && !IS_ROOT(dentry);
     341             : }
     342             : 
     343             : static inline int cant_mount(const struct dentry *dentry)
     344             : {
     345           0 :         return (dentry->d_flags & DCACHE_CANT_MOUNT);
     346             : }
     347             : 
     348             : static inline void dont_mount(struct dentry *dentry)
     349             : {
     350           0 :         spin_lock(&dentry->d_lock);
     351           0 :         dentry->d_flags |= DCACHE_CANT_MOUNT;
     352           0 :         spin_unlock(&dentry->d_lock);
     353             : }
     354             : 
     355             : extern void __d_lookup_unhash_wake(struct dentry *dentry);
     356             : 
     357             : static inline int d_in_lookup(const struct dentry *dentry)
     358             : {
     359          52 :         return dentry->d_flags & DCACHE_PAR_LOOKUP;
     360             : }
     361             : 
     362             : static inline void d_lookup_done(struct dentry *dentry)
     363             : {
     364           0 :         if (unlikely(d_in_lookup(dentry)))
     365           0 :                 __d_lookup_unhash_wake(dentry);
     366             : }
     367             : 
     368             : extern void dput(struct dentry *);
     369             : 
     370             : static inline bool d_managed(const struct dentry *dentry)
     371             : {
     372             :         return dentry->d_flags & DCACHE_MANAGED_DENTRY;
     373             : }
     374             : 
     375             : static inline bool d_mountpoint(const struct dentry *dentry)
     376             : {
     377           0 :         return dentry->d_flags & DCACHE_MOUNTED;
     378             : }
     379             : 
     380             : /*
     381             :  * Directory cache entry type accessor functions.
     382             :  */
     383             : static inline unsigned __d_entry_type(const struct dentry *dentry)
     384             : {
     385           5 :         return dentry->d_flags & DCACHE_ENTRY_TYPE;
     386             : }
     387             : 
     388             : static inline bool d_is_miss(const struct dentry *dentry)
     389             : {
     390           3 :         return __d_entry_type(dentry) == DCACHE_MISS_TYPE;
     391             : }
     392             : 
     393             : static inline bool d_is_whiteout(const struct dentry *dentry)
     394             : {
     395             :         return __d_entry_type(dentry) == DCACHE_WHITEOUT_TYPE;
     396             : }
     397             : 
     398             : static inline bool d_can_lookup(const struct dentry *dentry)
     399             : {
     400           1 :         return __d_entry_type(dentry) == DCACHE_DIRECTORY_TYPE;
     401             : }
     402             : 
     403             : static inline bool d_is_autodir(const struct dentry *dentry)
     404             : {
     405           0 :         return __d_entry_type(dentry) == DCACHE_AUTODIR_TYPE;
     406             : }
     407             : 
     408             : static inline bool d_is_dir(const struct dentry *dentry)
     409             : {
     410           0 :         return d_can_lookup(dentry) || d_is_autodir(dentry);
     411             : }
     412             : 
     413             : static inline bool d_is_symlink(const struct dentry *dentry)
     414             : {
     415           1 :         return __d_entry_type(dentry) == DCACHE_SYMLINK_TYPE;
     416             : }
     417             : 
     418             : static inline bool d_is_reg(const struct dentry *dentry)
     419             : {
     420           0 :         return __d_entry_type(dentry) == DCACHE_REGULAR_TYPE;
     421             : }
     422             : 
     423             : static inline bool d_is_special(const struct dentry *dentry)
     424             : {
     425             :         return __d_entry_type(dentry) == DCACHE_SPECIAL_TYPE;
     426             : }
     427             : 
     428             : static inline bool d_is_file(const struct dentry *dentry)
     429             : {
     430             :         return d_is_reg(dentry) || d_is_special(dentry);
     431             : }
     432             : 
     433             : static inline bool d_is_negative(const struct dentry *dentry)
     434             : {
     435             :         // TODO: check d_is_whiteout(dentry) also.
     436           3 :         return d_is_miss(dentry);
     437             : }
     438             : 
     439             : static inline bool d_flags_negative(unsigned flags)
     440             : {
     441           0 :         return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;
     442             : }
     443             : 
     444             : static inline bool d_is_positive(const struct dentry *dentry)
     445             : {
     446           3 :         return !d_is_negative(dentry);
     447             : }
     448             : 
     449             : /**
     450             :  * d_really_is_negative - Determine if a dentry is really negative (ignoring fallthroughs)
     451             :  * @dentry: The dentry in question
     452             :  *
     453             :  * Returns true if the dentry represents either an absent name or a name that
     454             :  * doesn't map to an inode (ie. ->d_inode is NULL).  The dentry could represent
     455             :  * a true miss, a whiteout that isn't represented by a 0,0 chardev or a
     456             :  * fallthrough marker in an opaque directory.
     457             :  *
     458             :  * Note!  (1) This should be used *only* by a filesystem to examine its own
     459             :  * dentries.  It should not be used to look at some other filesystem's
     460             :  * dentries.  (2) It should also be used in combination with d_inode() to get
     461             :  * the inode.  (3) The dentry may have something attached to ->d_lower and the
     462             :  * type field of the flags may be set to something other than miss or whiteout.
     463             :  */
     464             : static inline bool d_really_is_negative(const struct dentry *dentry)
     465             : {
     466             :         return dentry->d_inode == NULL;
     467             : }
     468             : 
     469             : /**
     470             :  * d_really_is_positive - Determine if a dentry is really positive (ignoring fallthroughs)
     471             :  * @dentry: The dentry in question
     472             :  *
     473             :  * Returns true if the dentry represents a name that maps to an inode
     474             :  * (ie. ->d_inode is not NULL).  The dentry might still represent a whiteout if
     475             :  * that is represented on medium as a 0,0 chardev.
     476             :  *
     477             :  * Note!  (1) This should be used *only* by a filesystem to examine its own
     478             :  * dentries.  It should not be used to look at some other filesystem's
     479             :  * dentries.  (2) It should also be used in combination with d_inode() to get
     480             :  * the inode.
     481             :  */
     482             : static inline bool d_really_is_positive(const struct dentry *dentry)
     483             : {
     484             :         return dentry->d_inode != NULL;
     485             : }
     486             : 
     487             : static inline int simple_positive(const struct dentry *dentry)
     488             : {
     489           0 :         return d_really_is_positive(dentry) && !d_unhashed(dentry);
     490             : }
     491             : 
     492             : extern void d_set_fallthru(struct dentry *dentry);
     493             : 
     494             : static inline bool d_is_fallthru(const struct dentry *dentry)
     495             : {
     496             :         return dentry->d_flags & DCACHE_FALLTHRU;
     497             : }
     498             : 
     499             : 
     500             : extern int sysctl_vfs_cache_pressure;
     501             : 
     502             : static inline unsigned long vfs_pressure_ratio(unsigned long val)
     503             : {
     504           0 :         return mult_frac(val, sysctl_vfs_cache_pressure, 100);
     505             : }
     506             : 
     507             : /**
     508             :  * d_inode - Get the actual inode of this dentry
     509             :  * @dentry: The dentry to query
     510             :  *
     511             :  * This is the helper normal filesystems should use to get at their own inodes
     512             :  * in their own dentries and ignore the layering superimposed upon them.
     513             :  */
     514             : static inline struct inode *d_inode(const struct dentry *dentry)
     515             : {
     516             :         return dentry->d_inode;
     517             : }
     518             : 
     519             : /**
     520             :  * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE()
     521             :  * @dentry: The dentry to query
     522             :  *
     523             :  * This is the helper normal filesystems should use to get at their own inodes
     524             :  * in their own dentries and ignore the layering superimposed upon them.
     525             :  */
     526             : static inline struct inode *d_inode_rcu(const struct dentry *dentry)
     527             : {
     528           0 :         return READ_ONCE(dentry->d_inode);
     529             : }
     530             : 
     531             : /**
     532             :  * d_backing_inode - Get upper or lower inode we should be using
     533             :  * @upper: The upper layer
     534             :  *
     535             :  * This is the helper that should be used to get at the inode that will be used
     536             :  * if this dentry were to be opened as a file.  The inode may be on the upper
     537             :  * dentry or it may be on a lower dentry pinned by the upper.
     538             :  *
     539             :  * Normal filesystems should not use this to access their own inodes.
     540             :  */
     541             : static inline struct inode *d_backing_inode(const struct dentry *upper)
     542             : {
     543           0 :         struct inode *inode = upper->d_inode;
     544             : 
     545             :         return inode;
     546             : }
     547             : 
     548             : /**
     549             :  * d_backing_dentry - Get upper or lower dentry we should be using
     550             :  * @upper: The upper layer
     551             :  *
     552             :  * This is the helper that should be used to get the dentry of the inode that
     553             :  * will be used if this dentry were opened as a file.  It may be the upper
     554             :  * dentry or it may be a lower dentry pinned by the upper.
     555             :  *
     556             :  * Normal filesystems should not use this to access their own dentries.
     557             :  */
     558             : static inline struct dentry *d_backing_dentry(struct dentry *upper)
     559             : {
     560             :         return upper;
     561             : }
     562             : 
     563             : /**
     564             :  * d_real - Return the real dentry
     565             :  * @dentry: the dentry to query
     566             :  * @inode: inode to select the dentry from multiple layers (can be NULL)
     567             :  *
     568             :  * If dentry is on a union/overlay, then return the underlying, real dentry.
     569             :  * Otherwise return the dentry itself.
     570             :  *
     571             :  * See also: Documentation/filesystems/vfs.rst
     572             :  */
     573             : static inline struct dentry *d_real(struct dentry *dentry,
     574             :                                     const struct inode *inode)
     575             : {
     576           0 :         if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
     577           0 :                 return dentry->d_op->d_real(dentry, inode);
     578             :         else
     579             :                 return dentry;
     580             : }
     581             : 
     582             : /**
     583             :  * d_real_inode - Return the real inode
     584             :  * @dentry: The dentry to query
     585             :  *
     586             :  * If dentry is on a union/overlay, then return the underlying, real inode.
     587             :  * Otherwise return d_inode().
     588             :  */
     589             : static inline struct inode *d_real_inode(const struct dentry *dentry)
     590             : {
     591             :         /* This usage of d_real() results in const dentry */
     592             :         return d_backing_inode(d_real((struct dentry *) dentry, NULL));
     593             : }
     594             : 
     595             : struct name_snapshot {
     596             :         struct qstr name;
     597             :         unsigned char inline_name[DNAME_INLINE_LEN];
     598             : };
     599             : void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
     600             : void release_dentry_name_snapshot(struct name_snapshot *);
     601             : 
     602             : #endif  /* __LINUX_DCACHE_H */

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